1. Field of the Invention
The present invention relates to a radio wave receiving apparatus in which antenna resolution is improved by using a transfer function in the azimuthal frequency domain of an antenna pattern.
2. Description of the Related Art
When observing target objects, for example, in using a radar, a method has been generally used in which the pointing direction of an antenna beam is changed, for example, by rotating the antenna to receive radio waves from the respective azimuths pointed at by the antenna beam, so as to observe the intensity of the received radio wave (antenna response) with respect to the azimuths. In doing so, the use of an antenna with a narrower beamwidth results in an antenna response approximating the distribution of the radio wave sources and, hence, improves the azimuth resolution of the radar. In the prior art, in order to, improve antenna resolution, it is necessary to obtain an antenna response which more closely approximates the distribution of the radio sources. Although another method is also known, such as in a synthetic aperture radar where antenna resolution is improved by subjecting the received radio wave to signal processing, this method, too, intends to obtain an antenna response approximating the distribution of the radio wave sources by achieving, through signal processing, and effect equivalent to that of reducing the antenna beamwidth.
The above conventional technique for improving the antenna resolution is a method of indirectly obtaining the distribution of the radio wave sources from the antenna response and there is a problem in that the distribution of the radio wave sources cannot be directly obtained. If there existed an antenna having its pattern represented by the Dirac delta function, the antenna response of such an antenna would correspond to the response of the radio wave sources. It is known from antenna theory, however, that an antenna having such a pattern does not exist. Accordingly, since an actual antenna pattern has a finite beamwidth and sidelobes, there is a problem that the distribution of the observable radio wave sources is distorted by the antenna pattern.